As far as I know, a trapezoid is defined as a quadrilateral with exactly one set of parallel sides. However, a very highly regarded educator and textbook author recently argued that this definition is incorrect. His definition of a trapezoid is that it is a quadrilateral that has at least one pair of parallel sides. A square, therefore, would be considered a trapezoid. Is he correct or are thousands of books going to be published with the wrong definition?

I assumed from the graph that the function had a limit at x=0 of 0,
but since it involves sin(1/0) I can not prove this using the basic
trigonometric limits (sin x/x and (1-cos x)/x), L'Hopital's
rule, or by rearranging the equation. Can you help?

Many students are taught that the imaginary unit i is equal to the
square root of -1. In fact, this informal definition often leads to
confusion. Here's a more formal definition of i which goes a long way
towards clearing up the misconceptions.